Conventionally, there is known a control device of a continuously variable transmission with an auxiliary transmission which performs a cooperative control by which a variator and a stepped transmission mechanism are simultaneously shifted (cf. for example, patent document 1).
In this case, “the cooperative control” is a shift by which a transmission gear ratio of the variator is varied in a direction opposite to a variation direction of the transmission gear ratio of the auxiliary transmission mechanism when a gear stage of the auxiliary transmission mechanism is varied. By the shift by this cooperative control, it is possible to suppress the sudden variation of the transmission gear ratio (hereinafter, referred to as “through transmission gear ratio”). It is possible to decrease the shift shock before and after the shift by the auxiliary transmission mechanism, and to suppress the unnatural feeling to the driver.
In this conventional device, in the cooperative control with the shift of the auxiliary transmission mechanism in the region (the low vehicle speed, the low opening degree) in which the input torque to the continuously variable transmission is relatively small, the variation of the engine speed before and after the shift is small relative to a region (the high vehicle speed and the high opening degree) in which the input torque is relatively large. With this, the feedback control may not function as desired. As the countermeasure, the cooperative shift inertia phase time period of the entire transmission is set. The cooperative control is performed so that the two shifts are finished during the cooperative shift inertia phase time period.
However, even when the cooperative shift inertia phase time period is set, the actual transmission gear ratio does not follow the through transmission gear ratio due to the variation of the hydraulic pressure and so on. The cooperative control may be thrown into disorder. In particular, in a case of the upshift in which the inertia progress speed of the variator is slow and the inertia progress speed of the auxiliary transmission mechanism is fast, the clutch capacity of the auxiliary transmission mechanism becomes excessively much. The transmission input rotation speed (=the driving source rotation speed such as the engine speed) is decreased.
It is, therefore, an object of the present invention to provide a control device with an auxiliary transmission which is devised to solve the above-described problems, and to suppress a variation of a transmission input rotation speed, and to improve drivability at a cooperative control with the shift of the auxiliary transmission mechanism.